The methods of three-dimensional X-ray crystal structure analysis will be used to determine quantitative aspects of metalloporphyrin stereochemistry. The synthesis, chemical and structural characterization of nitric oxide complexes of metalloporphyrins will be continued. Other metalloporphyrin derivatives to be studied include low-spin cobalt porphyrins and other metallorporphyrins detailing the effects of d-electron configuration on stereochemistry. Other derivatives to be studied include compounds in which the prophyrin ring itself is oxidized or reduced.